The present invention relates generally to particle pulse generation, and more particularly to the generation of intense particle beams via the coupling of large amounts of energy from an inductive store directly to an intense particle beam.
Intense particle beams are used in nuclear weapon effects simulation, target heating for inertial and magnetic confinment fusion, laser pumping, microwave and pulsed x-ray production, as injectors for high current accelorators, and in advanced weapons systems. The conventional techinque for producing intense electron and/or ion beams is to apply a sharp, high voltage pulse of very short duration to a pair of electrodes forming a diode. Typically, a capacitive energy store such as a capacitive pulse forming line will be used to provide the short duration, high voltage pulse to the diode. Systems of this type have been built and operated at upto megajoule energy levels, voltages of several megavolts and currents in excess of a megampere. However, such systems are quite large and expensive, primarily due to the electric field strength limitations on capacitive energy storage.
Magnetic compression of plasma is another method available for accelerating a particle beam. However, magnetic compression systems are inherently inefficient because particle (electron) acceleration is limited to a potential of no more than a few times that of the source voltage due to the inherent nature of the acceleration mechanism. Additionally, the beam extraction time is a small fraction of the period over which the compression occurs.
Additional methods bearing on the generation of particle streams also include those used to induce large currents in plasmas, the so-called, theta and toroidal pinches. The major components of the particle streams generated with these methods have low energies in comparison with the source voltage. In some cases a very small component of the stream attains high (run-away) velocity. In general, though, the theta and toroidal devices act like transformers efficiently coupling via their magnetic fields the stored energy from a capacitive bank external to the device to the plasma. In essence, the magnetic field of the device is used to couple energy from the electric field of the bank to kinetic energy of the particles. The low energies of the particles in these devices are the result of the high plasma density used in such devices. Additionally, the use of the closed plasma path in the toroidal pinch geometry also makes it impossible to extract the particle streams to a region external to the plasma.
A highly desirable alternative to the above set out methods is to use inductive energy storage to supply the energy to generate voltage pulses. Such inductive energy storage systems are limited only by the mechanical strength of the conductors in the system and can exceed the energy storage density of capacitive systems by factors of a thousand or more. Typically, in such systems primary energy sources such as rotating electrical machinery (homopolar generators, or pulse alternators, for example) or magnetodynamic systems (magnetic flux compression generators or pulsed MHD devices) may be utilized to supply current to a storage inductance. The use of such rotating electrical machinery as the primary energy source is especially advantageous in that such machines require significantly less volume that capacitor banks and are thus extremely compact. However, such current sources typically have rise-times on the order of 10.sup.1 -10.sup.-4 seconds which are much longer than the operating times of intense beam diodes (10.sup.-6 -10.sup.-7 seconds). Since these rise-times are significantly longer than that desired for driving intense beam diodes, the current must be carried by a separate auxiliary element during the time required for delivery of energy to the inductive store. Current flow in this auxiliary element must then be interrupted in order to direct energy into a diode connected in parallel with the auxiliary element to generate the actual intense beam pulse. For further discussion on this point, see the reference Pulsed High Magnetic Fields, by Heinz Knoepfel, American Elsevier Publishing Company, 1970 Chapter 6. Various problems arise in attempting to efficiently couple the energy from the inductive store to the diode in a short time in an efficient manner.